Alternative low water cut off to McDonnell Miller Series 69

[ShrimpBurrito]

My folks have an old American Standard oil steam boiler that has a McDonnell Miller Series 69 low water cut-off. A few weeks ago, they came back from a weekend getaway to find that the house was 40-something degrees because the boiler had not turned on due to the low water cut-off being corroded so much that it failed. He just installed that one brand new about 4 months ago. And the one before that didn't last very long, either.

The spec page for the cut-off is here:

http://www.mcdonnellmiller.com/prod/69lwco.pdf

Does anyone have any suggestions for something more durable, or perhaps some ideas of what he possibly could be doing wrong that leads to this premature failure?

Many thanks,
Dave